I have made multiple hats on my 40-peg round loom, but only with 6 weight yarn. Tried it with 5 weight and it's far more loose and gap-y than I want. Would
Loom Size , Hat Size and Number of Rows
Loom Lore: Brenda's Basic Baby Blanket
Knit a Slouchy Hat on a Round Loom : 12 Steps (with Pictures) - Instructables
How to Loom Knit a Hat - Life on Leetown
How to Loom Knit a Teddy Bear 36 pegs - YouTube
Ravelry: Easy Loom Knitted Hat With A Brim pattern by Crafting With Claudie